An end base structure of a conventional power stapler is shown in FIG. 1 and includes a cylinder 16 in the barrel 15 of the power stapler and a piston 18 with a piston rod 19 movably received in the cylinder 16. An end cap 11 is mounted to the rear end of the barrel 15 and has two tubular portions 110, 112 so that a frame 12 is movably engaged between the inside 111 of the tubular portion 110 and the outside of the other tubular portion 112. A seal part 120 is connected to the frame 12 and contacts against the distal end of the cylinder 16 so as to prevent high pressurized air from entering the cylinder 16 when the trigger (not shown) of the power stapler is not yet pulled. Two seals 125, 126 are respectively mounted to the frame 12 and engaged with the two tubular portions 110, 112. A flange 161 extends radially outward from the cylinder 16 and is engaged with the inside of the end cap 11. A fixed member 17 is enclosed by the tubular portion 112 and has a protrusion 17 extending toward the cylinder 16. A spring 13 is biased between the frame 12 and the fixed member 17 so as to push the frame 12 back to the cylinder 16 after the trigger is pulled. The piston 18 has a protrusion portion which extends through a central hole in the frame 12 and contacts the end surface 170 of the protrusion 17 of the fixed member 17.
When the user pulls the trigger, the frame 12 is moved away from the cylinder 16 to let pressurized air enter the cylinder 16 to eject the piston 18. After the piston 18 is ejected, the spring 13 pushes the frame 12 back to the cylinder 16 and the protrusion portion of the piston 18 will impact the end surface 170 of the protrusion 17 of the fixed member 17. An inherent shortcoming of the conventional power stapler is that the seals 125, 126, the seal part 120 and the end surface 170 of the fixed member 17 will be worn out for the frequent movements of the frame 12 and the piston 18. Leakage could happen between the surface and the seals 125, 126, and between the distal end of the cylinder 16 and the seal part 120.
The present invention intends to provide an end base of a power stapler wherein the frame has passages communicating with annular space where the seal part is engaged so as to form a lower pressure area at the inside of the seal part to securely position the seal part on the frame. The fixed member is not directly connected to the frame so that the movement of the frame is independent from the impact between the piston and the fixed member. The present invention has arisen to mitigate and obviate the disadvantages of the conventional power stapler.